As conventional drug delivery systems or molecular imaging probes for labeling specific body tissues, various polymer nano-particles have been reported which carry, encapsulate, or bind with drugs or fluorescent dyes.
For example, Patent Document 1 discloses, as a drug delivery system or molecular imaging probe intended to be directly intravenously administered, an amphiphilic block polymer having a hydrophilic polypeptide chain including 10 or more sarcosine units and a hydrophobic molecular chain including 5 or more amino acid units or hydroxy acid units as essential structural units.
Further, Patent Document 2 discloses, as a molecular imaging probe intended to be directly intravenously administered, a molecular assembly containing two polymers, one of which is an amphiphilic block polymer having a hydrophilic block chain including 20 or more sarcosine units and a hydrophobic block chain including 10 or more lactic acid units and the other is a labeled polymer having at least 10 or more lactic acid units and a labeling group.
Meanwhile, for the purpose of enhancing the activity of a bioactive component in the skin, a transdermal external preparation has been proposed which includes polymethyl methacrylate (PMMA) nano-particles encapsulating a bioactive component (Patent Document 3). As in the case of this transdermal external preparation, for the purpose of allowing a bioactive component to act in the skin, a transdermal external preparation has also been proposed which includes PLGA nano-particles encapsulating tranexamic acid (Patent Document 4).
However, when the external preparation disclosed in Patent Document 3 is repeatedly used as a drug or cosmetic for a long time, there is a fear that PMMA remaining in the skin has adverse effects because PMMA is not a biodegradable polymer material. Further, there is a possibility that when the size of the particles is reduced, it is difficult to encapsulate a drug in the particles.
In the case of the external preparation disclosed in Patent Document 4, the amount of tranexamic acid that can be encapsulated in the PLGA nano-particles is very small, and therefore it is necessary to administer a large amount of the preparation in order to deliver tranexamic acid to a layer deeper than the skin layer (dermis). Further, when a drug that causes skin irritation is used, there is a fear that the drug that is too much to be encapsulated in the drug carrier has adverse effects on the skin.